The broad objectives of this proposal are to describe dye sensitized photodynamic alteration of lobster giant axons at a detailed neurophysiological level and at the molecular level. An understanding of photodynamic alteration is interesting in its own right, but more importantly it is a tool with which to probe the molecular basis for excitation. Photodynamic alteration affects specific excitation parameters, as previous work by the investigator has shown. Sensitized photo-oxidations of proteins and amino acids has and is being studied intensively by photochemists. The present investigation will combine the voltage-clamp technique for studying membrane excitation with photochemical techniques to generate data linking excitation parameters with photo-oxidation of membrane molecules (probably proteins).